if else statement in shiny not working properly

Below is a script I've been working on. You will notice that the reactive statement, table_data(), is where the heavy lifting takes place. When you run the app, you will see all three filters are empty. They are suppose to be empty, but the rendered table should be producing a table that represents the filtered output in that final else if statement:

res <- df %>% group_by(level1) %>% summarise(total=sum(sales)), so when the app loads, the first thing you should see is this:

But it does not produce that. It produces an empty table. I'm struggling to understand what I'm doing incorrectly. Here is the script:

level1 <- c('1','1','1','1','1','1','2','2','2','2','2','2','3','3','3','3','3','3')
level2 <- c('1A','1A','1B','1B','1C','1C','2A','2A','2B','2B','2C','2C','3A','3A','3B','3B','3C','3C')
level3 <- c('Jones','Smith','Johnson','James','Evans','Long','Roth','Goldberg','Ramos','Winston','Levin','Jackson','Fishman','Drake','Quinn','Lackey','Scott','McGuire')
sales <- c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18)

df <- cbind(level1,level2,level3,sales) %>% as.data.frame() %>% mutate(level1 = as.character(level1), level2 = as.character(level2), level3 = as.character(level3), sales = as.integer(sales))

ui <- fluidPage(
  fluidRow(
    column(8,
           width = 10, offset = 1,
           tags$h3("Select Area"),
           panel(
            selectInput('lev1', label = 'Level 1', c(unique(sort(df$level1))), multiple = TRUE),
            uiOutput("level2"),
            uiOutput("level3")
           ),
           DT::dataTableOutput(outputId = "test")
    )
  )
)

server <- function(input, output, session) {

  output$level2 <- renderUI({
    selectizeInput("lev2", "Level 2", multiple = TRUE, c(unique(sort(df$level2[df$level1 ==input$lev1]))))
  }) 

  output$level3 <- renderUI({
    selectizeInput("lev3", "Level 3", multiple = TRUE, c(unique(sort(df$level3[df$level2 ==input$lev2]))))
  })


table_data <- reactive({

  if(!is.null(input$lev1) & is.null(input$lev2) & is.null(input$lev3)) #When lev1 is not null, but the other two are
    res <- df %>% filter(level1 %in% input$lev1) %>% group_by(level1,level2) %>% summarise(total=sum(sales))
  else
    if(is.null(input$lev1) | !is.null(input$lev1) & !is.null(input$lev2) & is.null(input$lev3)) #When lev2 is not null, lev3 is null, and lev1 can be either/or
      res <- df %>% filter(level2 %in% input$lev2) %>% group_by(level2,level3) %>% summarise(total=sum(sales))
    else
      if(is.null(input$lev1) | !is.null(input$lev1) & is.null(input$lev2) | !is.null(input$lev2) & !is.null(input$lev3)) #When lev3 is not null, lev1 can be either/or, and lev2 can be either/or
        res <- df %>% filter(level3 %in% input$lev3) %>% group_by(level1,level2,level3) %>% summarise(total=sum(sales))
      else
        if(is.null(input$lev1) & is.null(input$lev2) & is.null(input$lev3)) #When lev1 is null, lev2 is null, and lev3 is null (THIS ONE IS NOT WORKING CORRECTLY)
      res <- df %>% group_by(level1) %>% summarise(total=sum(sales))

})

output$test <- DT::renderDataTable({
  table_data()
})

}

shinyApp(ui,server)